The present invention relates to an organic thin-film transistor and a manufacturing method for the organic thin-film transistor.
With the spread of information terminal equipment, there are increasing needs for a flat panel display as a display for a computer. Further, with the progress of computerization, there are increasing opportunities wherein information which has so far been offered in a sheet of paper medium is electronized to be offered, and there are increasing needs for an electronic paper or digital paper as a display medium for a mobile that is thin and light in weight and can be carried easily.
In general, in a flat type display device, a display medium is formed by using an element wherein liquid crystal, organic EL or electrophoresis is used. In the case of this display medium, a leading technology is one that employs an active driving element composed of thin-film transistor (TFT) as an image driving element.
TFT element is manufactured by forming successively a semiconductor thin-film such as a-Si (amorphous silicon) or P-Si (poly silicon) on a glass substrate, or forming successively a metallic thin-film such as a source electrode, a drain electrode and a gate electrode on a substrate. For manufacturing of flat panel display using the TFT, highly accurate photolithograph process is generally needed in addition to a thin-film forming process requiring a vacuum system facilities such as CVD and spattering and a high temperature processing process, resulting in extremely high load including facility cost and running cost. In addition, recent needs for a large-sized screen for display make the cost to be extremely huge.
As a technology to compensate for demerit of the conventional TFT element, research and development of organic TFT element employing an organic semiconductor material are advanced intensively in recent years. Since this organic TFT element can be manufactured in a low temperature process, it is possible to use a resin substrate, which is light in weight and is hardly broken, and it is said that a flexible display employing a resin film as a support may be realized. Further, by using an organic semiconductor material, which can be manufactured by a wet process such as printing or coating under atmospheric pressure, it is possible to realize a display which is excellent in productivity and is extremely low in cost.
As a required condition in an organic TFT technology, there is given highly accurate patterning for a channel. In the aforesaid patent, TOKKAIHEI No. 10-190001 and TOKKAI No. 2000-307172, molding of a channel portion requires highly accurate photolithography which causes problems that patterning is difficult, and manufacturing processes are complicated and huge facilities are required in the processes accordingly, resulting in high cost. The invention makes highly accurate patterning to be possible in a simple way, and solves the aforesaid problems greatly.
Further, as an organic thin-film transistor, there is disclosed, for example, an all-polymer type organic TFT technology in WO01/47043. Though a simplified process by ink-jetting or coating is proposed, there are problems that carrier mobility of an element is low, gate voltage is high, an electric current value under the state of switching-on is low, and an ON/OFF value of an electric current is low.
Further, there is a problem that characteristics of a transistor are deteriorated by influences of a coating solvent used in the process and of a component contained in a developer solution in the processes succeeding the formation of an organic semiconductor layer, such as, for example, a coating process of light-sensitive resin material for patterning or a developing process for a light-sensitive resin layer.
To overcome the abovementioned drawbacks in conventional organic thin-film transistors and conventional methods for manufacturing them, it is an object of the present invention to provide an organic thin-film transistor, which is manufactured trough an accurate patterning process at low cost without requiring complicated manufacturing processes and in which carrier mobility is high, gate voltage can be lowered, an electric current value is high under the state of switching ON, an ON/OFF value of an electric current is high accordingly and driving frequency is high. Further, it is another object of the present invention to provide a manufacturing method for the organic thin-film transistor, which makes it possible to suppress the deterioration of the characteristics of the organic thin-film transistor.
Accordingly, to overcome the cited shortcomings, the abovementioned objects of the present invention can be attained by organic thin-film transistors and methods for fabricating them described as follow.
(1) An organic thin-film transistor fabricated on a substrate, comprising: a first insulating layer formed on the substrate; an organic semiconductor layer formed on the first insulating layer; a second insulating layer formed on the organic semiconductor layer; a first through-hole bored through the second insulating layer; a second through-hole bored through the second insulating layer; a source electrode embedded in the first through-hole, a depth of which is equal to or greater than a thickness of the second insulating layer so that the source electrode contacts the organic semiconductor layer; and a drain electrode embedded in the second through-hole, a depth of which is equal to or greater than a thickness of the second insulating layer so that the drain electrode contacts the organic semiconductor layer.
(2) The organic thin-film transistor of item 1, further comprising: a gate electrode embedded in the first insulating layer.
(3) The organic thin-film transistor of item 1, wherein the second insulating layer is made of a photosensitive material.
(4) The organic thin-film transistor of item 1, wherein the second insulating layer is a coating film formed by applying a solvent, which includs a water as a main ingredient.
(5) An organic thin-film transistor fabricated on a substrate, comprising: a first wiring electrode formed on the substrate; a second wiring electrode formed on the substrate; an organic semiconductor layer formed on the substrate so as to cover the first wiring electrode and the second wiring electrode; a first through-hole bored through the organic semiconductor layer in such a manner that a part of the first wiring electrode is exposed in the first through-hole; a second through-hole bored through the organic semiconductor layer in such a manner that a part of the second wiring electrode is exposed in the second through-hole; a source electrode embedded in the first through-hole so that the source electrode is electronically coupled to the first wiring electrode; a drain electrode embedded in the second through-hole so that the drain electrode is electronically coupled to the second wiring electrode; a gate insulating layer formed on the organic semiconductor layer so as to cover the organic semiconductor layer, the source electrode embedded in the first through-hole and the drain electrode embedded in the second through-hole; and a gate electrode formed on the gate insulating layer.
(6) An organic thin-film transistor fabricated on a substrate, comprising: a first wiring electrode formed on the substrate; a second wiring electrode formed on the substrate; an insulating layer formed on the substrate so as to cover the first wiring electrode and the second wiring electrode; an organic semiconductor layer formed on the insulating layer; a first through-hole bored through the insulating layer in such a manner that a part of the first wiring electrode is exposed in the first through-hole; a second through-hole bored through the insulating layer in such a manner that a part of the second wiring electrode is exposed in the second through-hole; a source electrode embedded in the first through-hole so that the source electrode is electronically coupled to the first wiring electrode; a drain electrode embedded in the second through-hole so that the drain electrode is electronically coupled to the second wiring electrode; a gate insulating layer formed on the organic semiconductor layer so as to cover the organic semiconductor layer, the source electrode embedded in the first through-hole and the drain electrode embedded in the second through-hole; and a gate electrode formed on the gate insulating layer.
(7) The organic thin-film transistor of item 6, wherein the first through-hole and the second through-hole are bored through both the insulating layer and the organic semiconductor layer.
(8) A method for fabricating an organic thin-film transistor on a substrate, comprising the steps of: forming a gate electrode on a substrate; forming a first insulating layer on the substrate so as to cover the gate electrode; forming an organic semiconductor layer on the first insulating layer; forming a second insulating layer on the organic semiconductor layer; boring a first through-hole through the second insulating layer; boring a second through-hole through the second insulating layer; embedding a source electrode into the first through-hole, a depth of which is equal to or greater than a thickness of the second insulating layer so that the source electrode contacts the organic semiconductor layer; and embedding a drain electrode into the second through-hole, a depth of which is equal to or greater than a thickness of the second insulating layer so that the drain electrode contacts the organic semiconductor layer.
(9) The method of item 8, wherein, in the embedding steps for both the source electrode and the drain electrode, ink particles, of a solution or a dispersion liquid containing an electrode material, are emitted into the first through-hole and the second through-hole by employing an ink-jetting method for patterning source electrodes and drain electrodes.
(10) The method of item 8, wherein the second insulating layer is made of a photosensitive material.
(11) The method of item 8, wherein the second insulating layer is a coating film formed by applying a solvent, which includes a water as a main ingredient.
(12) A method for fabricating an organic thin-film transistor on a substrate, comprising the steps of: forming a first wiring electrode on the substrate; forming a second wiring electrode on the substrate; forming an organic semiconductor layer on the substrate so as to cover both the first wiring electrode and the second wiring electrode; boring a first through-hole through the organic semiconductor layer in such a manner that a part of the first wiring electrode is exposed in the first through-hole; boring a second through-hole through the organic semiconductor layer in such a manner that a part of the second wiring electrode is exposed in the second through-hole; embedding a source electrode into the first through-hole so that the source electrode is electronically coupled to the first wiring electrode; embedding a drain electrode into the second through-hole so that the drain electrode is electronically coupled to the second wiring electrode; forming a gate insulating layer on the organic semiconductor layer so as to cover the organic semiconductor layer, the source electrode embedded in the first through-hole and the drain electrode embedded in the second through-hole; and forming a gate electrode on the gate insulating layer.
(13) The method of item 12, wherein, in the embedding steps for both the source electrode and the drain electrode, ink particles, of a solution or a dispersion liquid containing an electrode material, are emitted into the first through-hole and the second through-hole by employing an ink-jetting method for patterning source electrodes and drain electrodes.
(14) A method for fabricating an organic thin-film transistor on a substrate, comprising the steps of: forming a first wiring electrode on the substrate; forming a second wiring electrode on the substrate; forming an insulating layer on the substrate so as to cover the first wiring electrode and the second wiring electrode; forming an organic semiconductor layer on the insulating layer; boring a first through-hole through the insulating layer in such a manner that a part of the first wiring electrode is exposed in the first through-hole; boring a second through-hole through the insulating layer in such a manner that a part of the second wiring electrode is exposed in the second through-hole; embedding a source electrode into the first through-hole so that the source electrode is electronically coupled to the first wiring electrode; embedding a drain electrode into the second through-hole so that the drain electrode is electronically coupled to the second wiring electrode; forming a gate insulating layer on the organic semiconductor layer so as to cover the organic semiconductor layer, the source electrode embedded in the first through-hole and the drain electrode embedded in the second through-hole; and forming a gate electrode on the gate insulating layer.
(15) The method of item 14, wherein, in the boring steps for the first through-hole and the second through-hole, the first through-hole and the second through-hole are bored through both the insulating layer and the organic semiconductor layer.
(16) The method of item 14, wherein, in the embedding steps for both the source electrode and the drain electrode, ink particles, of a solution or a dispersion liquid containing an electrode material, are emitted into the first through-hole and the second through-hole by employing an ink-jetting method for patterning source electrodes and drain electrodes.
Further, to overcome the abovementioned problems, other organic thin-film transistors and methods for manufacturing them, embodied in the present invention, will be described as follow:
(17) An organic thin-film transistor characterized in that the organic thin-film transistor is formed by a through hole portion touching an organic semiconductor channel, and a source electrode and a drain electrode are formed to be at least an insulation layer.
(18) An organic thin-film transistor characterized in that the organic thin-film transistor is composed of a support and of layers, through holes and electrodes which are arranged on the support, such as a gate insulation layer, an organic semiconductor layer and a second insulation layer which are provided on the gate electrode, two through holes passing through the second insulation layer and a source electrode and a drain electrode which are embedded respectively in the through holes and are cemented to the organic semiconductor layer.
(19) An organic thin-film transistor characterized in that the organic thin-film transistor is composed of a support and of layers, through holes and electrodes which are arranged on the support, such as a first and second electrodes, an organic semiconductor layer provided on the aforesaid two electrodes, two through holes passing through the organic semiconductor layer and touching respectively the first and second electrodes, a source electrode and a drain electrode both embedded in the through holes and are cemented respectively to the organic semiconductor layer, the first electrode and the second electrode, a gate insulation layer formed on the structure, and a gate electrode formed on the gate insulation layer.
(20) An organic thin-film transistor characterized in that the organic thin-film transistor is composed of a support and of electrodes, layers and through holes which are arranged on the support, such as a first and second electrodes, an insulation layer provided on the aforesaid two electrodes, an organic semiconductor layer, two through holes passing through at least the insulation layer and touching respectively the first and second electrodes, a source electrode and a drain electrode both embedded in the through holes and are cemented respectively to the organic semiconductor layer, the first electrode and the second electrode, a gate insulation layer formed on the structure, and a gate electrode formed on the gate insulation layer.
(21) An organic thin-film transistor characterized in that the organic thin-film transistor is composed of a support and of electrodes, layers and through holes which are arranged on the support, such as a first and second electrodes, an insulation layer provided on the aforesaid two electrodes, an organic semiconductor layer, two through holes passing through at least the insulation layer and the organic semiconductor layer and touching respectively the first and second electrodes, a source electrode and a drain electrode both embedded in the through holes and are cemented respectively to the organic semiconductor layer, the first electrode and the second electrode, a gate insulation layer formed on the structure, and a gate electrode formed on the gate insulation layer.
(22) A manufacturing method, for an organic thin-film transistor, characterized in that a gate electrode is provided on a support on which a gate insulation layer, an organic semiconductor layer and a second insulation layer are formed successively, then, two through holes passing through the second insulation layer and touching the organic semiconductor layer are formed, and a source electrode and a drain electrode are embedded in the through holes so that these electrodes may be cemented to the organic semiconductor layer.
(23) A manufacturing method, for an organic thin-film transistor, characterized in that a first electrode and a second electrode are provided on a support, an organic semiconductor layer is formed on the electrode, two through holes that pass through the organic semiconductor layer and touch respectively the first electrode and the second electrode are formed, then, a source electrode and a drain electrode are embedded in the through holes in a way that these electrodes are cemented respectively to the organic semiconductor layer, the first electrode and the second electrode, then, gate insulation layers are formed respectively on the source electrode and the drain electrode, and a gate electrode is further provided on the gate insulation layer.
(24) A manufacturing method, for an organic thin-film transistor, characterized in that a first electrode and a second electrode are provided on a support, an insulation layer and an organic semiconductor layer are formed on the aforesaid electrodes in succession, two through holes that pass through at least the insulation layer and touch respectively the first electrode and the second electrode are formed, a source electrode and a drain electrode are embedded in the through holes in a way that these electrodes are cemented to the organic semiconductor layer, the first electrode and the second electrode, an organic semiconductor layer and a gate insulation layer are formed in succession respectively on the source electrode and the drain electrode, and a gate electrode is provided on the gate insulation layer.
(25) A manufacturing method, for an organic thin-film transistor, characterized in that a first electrode and a second electrode are provided on a support, an insulation layer and an organic semiconductor layer are formed on the aforesaid electrodes in succession, two through holes that pass through at least the insulation layer and the organic semiconductor layer and touch respectively the first electrode and the second electrode, then, a source electrode and a drain electrode are embedded in the through holes in a way that the electrodes are cemented respectively to the organic semiconductor layer, the first electrode and the second electrode.